The Experts below are selected from a list of 279 Experts worldwide ranked by ideXlab platform
Andrzej Duda - One of the best experts on this subject based on the ideXlab platform.
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Fluorescence study of the dynamics of a star-shaped poly(ε-caprolactone)s in THF: A comparison with a star-shaped poly(l-lactide)s
Polymer, 2009Co-Authors: Martin Danko, Jan Libiszowski, Marian Wolszczak, Dusan Racko, Andrzej DudaAbstract:Molecular dynamics of 2-, 4- and 6-arm star-shaped poly(ε-caprolactone)s (PCLs) functionalized with pyrene at all chain ends followed by excimer formation were investigated in THF as a solvent. Dilute solutions (10-8 to 10-6 mol L-1) of these polymers revealed excimer emission due to the intramolecular cyclization, proceeding via chain end interaction. Time-resolved fluorescence measurements of star-shaped PCLs showed complex decay profiles of monomer and excimer fluorescence. An intensity rise component of decay profiles monitored in excimer region (500 nm) was observed for star-shaped polymers due to dynamic formation of Excimers. Dipyrene-PCL (2-arm) also showed partial formation of static pyrene Excimers as followed from measurement of excitation spectra at ambient temperature in THF. Excimer intensity of di- and four pyrene-telechelic PCLs was found to be comparable with that of di- and four pyrene-telechelic polylactide (PLA) polyesters having similar molar masses. 6-Arm PCL showed depressed excimer formation with regard to 6-arm PLA under the otherwise identical conditions contrary to the conclusion expected from the higher flexibility of the PCL chain. Eventually, molecular dynamic simulations showed that possible explanation can be related to different conformations of 6-arm PLA versus PCL stars. © 2009 Elsevier Ltd. All rights reserved.
Ulrich Kogelschatz - One of the best experts on this subject based on the ideXlab platform.
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high intensity sources of incoherent uv and vuv excimer radiation for low temperature materials processing
Applied Surface Science, 2000Co-Authors: Ulrich Kogelschatz, Hilmar Dr Esrom, J Y Zhang, Ian W BoydAbstract:The principles and properties of ultraviolet (UV) and vacuum ultraviolet (VUV) radiation generated by decaying excimer complexes are discussed. Excimer lamps offer high-intensity narrow-band radiation at various UV and VUV wavelengths and reach high efficiencies. They can provide high photon fluxes over extended areas. The use of Excimers offers several advantages: Excimers can be extremely efficient energy converters transforming electron kinetic energy into UV radiation. No self-absorption is observed in excimer systems. In most cases, excimer forming gas mixtures exhibit one dominant narrow emission band. Excimer systems can be pumped at extremely high power densities before saturation effects start to limit the spontaneous emission. Thus, extremely bright UV and VUV sources can be built. Different types of excimer lamps can be fabricated utilising, repetitively pulsed high power discharges, microwave discharges and dielectric-barrier discharges (silent discharges). For large-scale industrial applications dielectric-barrier discharges using fairly simple discharge configurations currently represent the most mature excimer lamp technology. Recent applications of excimer lamps include photo-deposition of large area or patterned thin metal films, of high- and low-dielectric constant insulating layers, photo-assisted low-temperature oxidation of Si, SiGe and Ge, UV curing, polymer etching and microstructuring of polymer surfaces. Applications investigated so far clearly demonstrate that low cost, high power excimer lamp systems can provide an interesting alternative to excimer lasers for industrial large-scale low-temperature materials processing.
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silent discharges for the generation of ultraviolet and vacuum ultraviolet excimer radiation
Pure and Applied Chemistry, 1990Co-Authors: Ulrich KogelschatzAbstract:Excimers, known from electron beam experiments and UV lasers, can also fomi in silent discharges, a discharge type used for large-scale ozone production. In this high pressure non-equilibrium discharge a dielectric barrier leads to the formation of localized short-lived microdischarges. Inside the microdischarge filaments energetic electrons can excite rare gas (RG) atoms which, under appropriate conditions, react to form RG/RG dimers or RG/halogen dimers. With the pure RG dimers Ar2*, Kr2*, Xe2*, their chlorides ArCl*, KrCl*, XeCl* and their fluorides ArF*, KrF*, XeF* a number of narrow-band UV sources can be obtained in the wavelength region between 120 nm and 360 nm. The physical parameters of the microdischarges and the reaction kinetics of excimer formation in silent discharges are discussed. The potential of these new UV sources for industrial UV processing is demonstrated. As an example of an application for such incoherent excimer UV sources structured and large-area metal deposition induced by the 172 nm radiation from a silent discharge in xenon is shown. Patterned thin palladium films could be produced by irradiating a palladium acetate coating through a contact mask. In a second step thicker copper layers were deposited on top of the palladium patterns by an elec@oless plating process.
Nitin Chattopadhyay - One of the best experts on this subject based on the ideXlab platform.
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differential forster resonance energy transfer from the Excimers of poly n vinylcarbazole to coumarin 153
Journal of Physical Chemistry B, 2012Co-Authors: Debanjana Ghosh, Nilashis Nandi, Nitin ChattopadhyayAbstract:Photophysics of the nonconjugated vinyl polymer poly(N-vinylcarbazole) (PNVC) has been explored in the presence of coumarin 153 (C153) exploiting steady state and time-resolved fluorometric techniques. Dual emission from the two distinct Excimers of PNVC adds importance to the study and makes it interesting. The study substantiates the occurrence of Forster resonance energy transfer (FRET) from PNVC to C153. The differential involvement of the two Excimers in the energy transfer process has been established. Considering the fact that FRET is a long distance dipole induced phenomenon, this differential effect has been rationalized from a difference in the dipole moments of the two Excimers. Determination of the quenching constants reveals an order of magnitude more quenching of the high energy excimer than the low energy one in the presence of the quencher C153.
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characterization of the Excimers of poly n vinylcarbazole using tranes
Journal of Luminescence, 2011Co-Authors: Debanjana Ghosh, Nitin ChattopadhyayAbstract:Time-resolved emission spectra (TRES) and time-resolved area normalized emission spectra (TRANES) are exploited to characterize the Excimers of poly(N-vinylcarbazole) (PNVC) in toluene and water. The time-resolved study together with the steady state measurements, decipher the fluorescence of the system containing pendant carbazole moieties in the polymer backbone unambiguously. Isoemissive point in the TRANES establishes that there are only two Excimers of PNVC, the partially overlapped excimer emitting at high energy and the sandwich type excimer emitting at lower energy, and they are formed exclusively in the photoexcited state. The study substantiates an equilibrium between the two Excimers.
Ryuzi Katoh - One of the best experts on this subject based on the ideXlab platform.
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origin of the stabilization energy of perylene excimer as studied by fluorescence and near ir transient absorption spectroscopy
Journal of Photochemistry and Photobiology A-chemistry, 2001Co-Authors: Ryuzi Katoh, Shigeo Murata, Subrata Sinha, Masanori TachiyaAbstract:Abstract The origin of the stabilization energy of perylene excimer in toluene has been studied. In order to measure the fluorescence spectra and its decay profiles under the condition free from the reabsorption effect, we designed a thin optical cell with a path length of about 10 μm. From the results, the photophysical parameters of perylene excimer such as the formation rate constant, the peak position and the lifetime and the quantum yield of fluorescence can be obtained. Using these values, the binding energy of perylene excimer can be evaluated as 0.44 eV from the temperature dependence of the transient absorption. By analyzing the band shape of the charge transfer absorption in near-IR wavelength range, the transfer integral V between a neutral excited state and an ion-pair state can be estimated as 0.37 eV. From these results, we conclude that the stabilization energy of perylene excimer consists of two components: exciton interaction (70%) and charge transfer interaction (30%). We also discuss the origin of the stabilization energy of other aromatic Excimers on the basis of the results on perylene excimer.
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near ir absorption spectrum of aromatic Excimers
Journal of Physical Chemistry A, 1997Co-Authors: Ryuzi Katoh, Eriko Katoh, Nana Nakashima, Miki Yuuki, Masahiro KotaniAbstract:The absorption spectrum of Excimers in fluid media has been measured with 1-methylnaphthalene, anthracene, pyrene, and perylene. In all compounds studied an absorption band characteristic of an excimer has been observed in the near-IR. It is shown that the IR band can be understood by assuming that an excimer is essentially a charge-transfer complex: The near-IR band is to be assigned to a transition from the lowest excimer state to a higher state which has an ion-pair character.
Shuizhu Wu - One of the best experts on this subject based on the ideXlab platform.
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a ratiometric fluorescent probe for hyaluronidase detection via hyaluronan induced formation of red light emitting Excimers
Biosensors and Bioelectronics, 2016Co-Authors: Qinghua Hu, Fang Zeng, Shuizhu WuAbstract:Abstract Hyaluronidase (HAase), which is involved in various physiological and pathological processes, can selectively degrade hyaluronan (HA) into small fragments, and it has been reported as a diagnostic and prognostic biomarker for bladder cancer. Herein, a facile ratiometric fluorescent sensing system for HAase has been developed, which is based on hyaluronan-induced formation of red-light emitting Excimers and can realize sensitive detection of HAase with a detection limit of 0.007 U/mL. A positively-charged pyrene analog (N-Py) has been synthesized and then mixed with the negatively-charged HA, due to electrostatic interaction between the two components, aggregation along with the N-Py Excimers readily form which emits red light. While in the presence of HAase, the enzyme catalyzes the hydrolysis of HA into small fragments, which in turn triggers disassembly of Excimers; consequently the N-Py excimer emission turns into monomer emission. The emission ratio resulted from the excimer–monomer transition can be used as the sensing signal for detecting HAase. The probe features visible-light excitation and red light emission (excimer), which is conducive to reducing possible interference from autofluorescence of biological samples. Furthermore, the assay system can be successfully used to determine HAase in human urine samples with satisfactory accuracy. This strategy may provide a suitable sensitive and accurate assay for HAase as well as an effective approach for developing fluorescent ratiometric assays for other enzymes.
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ratiometric fluorescent probe for alkaline phosphatase based on betaine modified polyethylenimine via excimer monomer conversion
Analytical Chemistry, 2014Co-Authors: Fangyuan Zheng, Fang Zeng, Jun Li, Shuizhu WuAbstract:Alkaline phosphatase (ALP) is an important diagnostic indicator for a number of human diseases since abnormal level of ALP is closely related to a variety of pathological processes; hence, the development of convenient and reliable assay methods for monitoring ALP is of great significance for medical sciences as well as biological diagnostics. Herein, we report the first ratiometric fluorescent sensing system for ALP. This sensing system consists of two components: the betaine-modified and positively charged polyethylenimine (PEI) and the negatively charged pyrene derivative containing one ALP-responsive phosphate group (Py-P, an aliphatic phosphate ester). In the absence of ALP, the two-component sensing system shows the excimer’s emission of Py-P, since Py-P molecules complex with the positively charged polyelectrolyte via electrostatic interactions, leading to the formation of pyrene Excimers. While in the presence of ALP, the phosphate moieties are cleaved from Py-P molecules due to the enzymatic reac...
